Endothelial dysfunction is a major contributor to the pathogenesis of coronary artery disease and a potential therapeutic target to improve myocardial perfusion in ischemic heart disease. The role of regular exercise in the improvement of endothelial dysfunction has garnered increasing attention from both researchers and clinicians as a mechanism by which myocardial perfusion and function can be substantially improved in patients with coronary artery disease. However, the mechanisms by which exercise training reverses endothelium dysfunction are not well defined. The overall goal of the research proposed in this application is to define the specific cellular/molecular mechanisms responsible for exercise training-induced improvements in endothelium function in collateral-dependent coronary arteries and arterioles of chronically occluded hearts. Our central hypothesis is that exercise training restores endothelium-dependent vasodilatation in coronary artery disease via enhanced nitric oxide bioavailability. Specifically, Specific Aim 1 will determine the effects of exercise training on cellular and molecular mechanisms responsible for endothelium-derived nitric oxide production in collateral-dependent coronary arteries and arterioles;Specific Aim 2 will determine the effects of exercise training on the role of reactive oxygen species in agonist-mediated, nitric oxide-dependent relaxation in collateral-dependent coronary arteries and arterioles;Specific Aim 3 will determine the effects of exercise training on the interaction of nitric oxide bioavailability and Rho-kinase activity in collateral-dependent coronary arteries of occluded hearts. To address these issues, we will determine the effects of exercise training on vascular endothelial function in the well-established porcine model of chronic coronary artery occlusion. These studies will examine functional vasomotor reactivity to endotheliumdependent vasodilators, protein and mRNA expression of enzymes and factors that contribute to endothelium function, and intracellular free calcium concentration and nitric oxide production in endothelial cells. Relevance: Coronary artery disease produces more than 50% of cardiovascular disease-related deaths, the preeminant health problem of developed countries worldwide. The research proposed in this application will determine the adaptations by which exercise/physical activity improves the function of the coronary arteries and thereby increases blood flow to compromised areas of the heart in diseased patients.